1. Field of the Invention
The present invention relates to a burner for industrial furnaces.
Swedish Patent Specification No. 9800473-2describes a method of cleansing the waste gases from a gas burner or some other combustion source, such as oil-fired burners, or the exhaust gases from internal combustion engines. The invention also relates to a gas burner in which the method is employed.
2. Description of the Related Art
It is usual to heat industrial furnaces with the aid of gas burners. The fuel normally used is natural gas, although other gases may be used, such as propane, butane and liquefied petroleum gas or bottled gas.
An example of an effective gas burner is a burner of the type where the burner head is placed in one end of an inner pipe around which there is placed an outer protective pipe which is closed at its bottom. The combustion gases or flue gases leaving the burner chamber pass into the inner pipe and down towards the bottom of the outer pipe, where they turn to flow between the outer pipe and the inner pipe in the opposite direction and then into a waste gas channel which leads to the surroundings. The protective pipe delivers heat to a furnace space by convection, corresponding to 30%, and by radiation, corresponding to 70%.
A similar type of burner also comprises an inner pipe and an outer protective pipe which surrounds the inner pipe. However, in this case the bottom of the protective pipe is not closed. The protective pipe is curved, for instance in a U-shape configuration, and the free end of the protective pipe is connected to an exhaust gas or waste gas channel. The inner pipe equipped with the burner head is straight and is thus located within the straight section of the protective pipe.
It is desirable to maintain the outer pipe at a temperature of up to 1150-1200xc2x0 C. so as to thereby enhance the power concentration of the burner. This is possible to achieve by producing the outer pipe from a high temperature material, such as silicon carbide (SiC) or APM. APM is an acronym of Advanced Powder Metallurgy, and the material contains about 73% Fe, 22% Cr, and 5% Al. The powder material is extruded into a tubular form.
According to this patent specification, gaseous fuel is introduced into one inlet and air is introduced into a separate inlet. It has been found that combustion will be more complete when the fuel is well mixed with the air of combustion. For this reason, it is proposed in accordance with this prior patent publication that a certain amount of air is delivered to the fuel inlet together with the fuel, while the remainder of the air of combustion is delivered through its own inlet. Because air is delivered to the fuel externally of the burner, this solution is encumbered with many drawbacks.
One drawback is that an explosive mixture of fuel and air may be present outside the actual burner, due to leakage downstream of the location at which fuel and air are mixed.
Another drawback is that the solution requires the use of several conduits, namely a fuel conduit and two air conduits connected to the burner. This results in confined spaces that make it difficult to carry out maintenance and servicing operations.
A third and decisive drawback is that the pre-mixture of air and fuel produced in the manner described in the patent specification has been found not to provide a maximum yield with respect to burner efficiency.
These drawbacks are avoided with the present invention.
The present invention thus relates to a gas burner of the type with which a burner head is placed in an inner pipe which is surrounded by an outer protective pipe. Waste gases from the burner head pass inside the inner pipe and then into the outer pipe, and thereafter into a waste gas channel which leads to the surroundings. Fuel is delivered to the burner head through a first conduit placed within the inner pipe, wherein air of combustion is delivered to the burner head through the space inwardly of the inner surface of the inner pipe. The first conduit terminates short of the burner head; in that the barrel surface of said conduit is perforated with holes, and a further pipe surrounds at least the perforated part of said conduit. One end of said further pipe extends to the burner head, whereas the other end of said further pipe is sealed against said conduit such as to form a mixing chamber between the outer surface of the conduit and the inner surface of said further pipe. A second conduit is connected to the barrel surface of said further pipe and is adapted to conduct a given amount of air to the mixing chamber.